This invention relates to a magnetron, more particularly to a magnetic contacting structure between a magnet and a yoke.
A magnetron is used generally as the power source of a microwave oven or a radar system. Microwave power is supplied to the oven or the radar system through an opening in an oven wall or a wave guide connected to the magnetron. The size of the opening in existing microwave ovens and radar systems has been large because of the large size of conventional magnetrons.
In recent years, the magnetron has been miniaturized for use in microwave ovens without reduction of performance. However, the opening in many microwave ovens remains large compared with the small size of the miniaturized magnetrons. In this latter case, as generally known in the art, a gasket is positioned between the opening of the oven and the magnetron to adjust for the large size of the opening. The gasket electrically connects the magnetron anode to the opening of the oven.
An internal magnet type magnetron has annular ferrite magnets at both sides of the magnetron anode, i.e., magnets are positioned adjacent output and input portions. A yoke, which together with the magnets forms a magnetic circuit, surrounds the magnets and the anode. The output portion of the magnetron extends through an opening in the annular magnet and an opening in the yoke. The diameter of the opening of the magnet is substantially equal to the output portion diameter, while the diameter of the yoke opening is larger than the diameter of the opening of the magnet. As known in the art, the gasket is positioned in the yoke opening adjacent the magnet. The yoke opening is also slightly larger than the opening of the oven so that the portion of the oven which forms the oven can be connected to the gasket.
Several disadvantages result from the conventional techniques of using a miniaturized magnetron in a microwave oven. For example, when the outer diameter of the magnet is reduced by miniaturizing the magnetron, the contact area of the magnet and the yoke is reduced. As a result, the magnetic flux from the magnet passing through the yoke is reduced. Further more, the magentic flux can fluctuate due to the magnetic or non-magnetic walls of the oven.
Finally, in U.S. Pat. No. 4,044,279 issued to Tsuzurahara on Aug. 23, 1977, an annular conductive washer is placed between the gasket and the magnet in order to prevent the loss of microwave power. However, a disadvantage of this conventional technique is that an air gap is formed between the yoke and the magnet. The air gap causes a reduction in the magnetic conductance of the magnetic circuit of the magnetron.